Added aws_managed_encryption option

Added aws_managed_encryption option for: https://github.com/danilop/yas3fs/issues/33
noted option for aws encryption

noted option for aws encryption
added recheck-s3 option doc

fixed doc for recheck-s3 option https://github.com/danilop/yas3fs/issues/30
fix for AES256 crypto on mkdir/symlink ops

fix for AES256 crypto on mkdir/symlink ops
Merge pull request #34 from bitsofinfo/master

added aws-managed-encryption option for AES256 issue #33, fixed README #30